hydration

1:  the act or process of combining or treating with water: asa:  the introduction of additional fluid into the body hydration sometimes helps to reduce the concentration of toxic substances in the tissuesb:  a chemical reaction in which water takes part with the formation of only one product hydration of ethylene to ethyl alcohol; especially :  a reaction in which water takes part in the form of intact molecules

2:  the quality or state of being hydrated; especially :  the condition of having adequate fluid in the body tissues